/* md5.c - MD5 Message-Digest Algorithm
 * Copyright (C) 1995, 1996, 1998, 1999,
 *               2000, 2001 Free Software Foundation, Inc.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation; either version 3, or (at your option) any
 * later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see <http://www.gnu.org/licenses/>.
 *
 * According to the definition of MD5 in RFC 1321 from April 1992.
 * NOTE: This is *not* the same file as the one from glibc.
 */
/* Written by Ulrich Drepper <drepper@gnu.ai.mit.edu>, 1995.  */
/* Heavily modified for GnuPG by <wk@gnupg.org> */

/* Test values:
 * ""                  D4 1D 8C D9 8F 00 B2 04  E9 80 09 98 EC F8 42 7E
 * "a"                 0C C1 75 B9 C0 F1 B6 A8  31 C3 99 E2 69 77 26 61
 * "abc                90 01 50 98 3C D2 4F B0  D6 96 3F 7D 28 E1 7F 72
 * "message digest"    F9 6B 69 7D 7C B7 93 8D  52 5A 2F 31 AA F1 61 D0
 */

#include <config.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include "util.h"
#include "memory.h"
#include "algorithms.h"

#include "bithelp.h"


typedef struct {
    u32 A,B,C,D;	  /* chaining variables */
    u32  nblocks;
    byte buf[64];
    int  count;
} MD5_CONTEXT;


static void
md5_init( MD5_CONTEXT *ctx )
{
    ctx->A = 0x67452301;
    ctx->B = 0xefcdab89;
    ctx->C = 0x98badcfe;
    ctx->D = 0x10325476;

    ctx->nblocks = 0;
    ctx->count = 0;
}




/* These are the four functions used in the four steps of the MD5 algorithm
   and defined in the RFC 1321.  The first function is a little bit optimized
   (as found in Colin Plumbs public domain implementation).  */
/* #define FF(b, c, d) ((b & c) | (~b & d)) */
#define FF(b, c, d) (d ^ (b & (c ^ d)))
#define FG(b, c, d) FF (d, b, c)
#define FH(b, c, d) (b ^ c ^ d)
#define FI(b, c, d) (c ^ (b | ~d))

static void
burn_stack (int bytes)
{
    char buf[128];
    
    wipememory(buf,sizeof buf);
    bytes -= sizeof buf;
    if (bytes > 0)
        burn_stack (bytes);
}



/****************
 * transform n*64 bytes
 */
static void
/*transform( MD5_CONTEXT *ctx, const void *buffer, size_t len )*/
transform( MD5_CONTEXT *ctx, byte *data )
{
    u32 correct_words[16];
    u32 A = ctx->A;
    u32 B = ctx->B;
    u32 C = ctx->C;
    u32 D = ctx->D;
    u32 *cwp = correct_words;

#ifdef BIG_ENDIAN_HOST
    { int i;
      byte *p2, *p1;
      for(i=0, p1=data, p2=(byte*)correct_words; i < 16; i++, p2 += 4 ) {
	p2[3] = *p1++;
	p2[2] = *p1++;
	p2[1] = *p1++;
	p2[0] = *p1++;
      }
    }
#else
    memcpy( correct_words, data, 64 );
#endif


#define OP(a, b, c, d, s, T)					    \
  do								    \
    {								    \
      a += FF (b, c, d) + (*cwp++) + T; 	    \
      a = rol(a, s);						    \
      a += b;							    \
    }								    \
  while (0)

    /* Before we start, one word about the strange constants.
       They are defined in RFC 1321 as

       T[i] = (int) (4294967296.0 * fabs (sin (i))), i=1..64
     */

    /* Round 1.  */
    OP (A, B, C, D,  7, 0xd76aa478);
    OP (D, A, B, C, 12, 0xe8c7b756);
    OP (C, D, A, B, 17, 0x242070db);
    OP (B, C, D, A, 22, 0xc1bdceee);
    OP (A, B, C, D,  7, 0xf57c0faf);
    OP (D, A, B, C, 12, 0x4787c62a);
    OP (C, D, A, B, 17, 0xa8304613);
    OP (B, C, D, A, 22, 0xfd469501);
    OP (A, B, C, D,  7, 0x698098d8);
    OP (D, A, B, C, 12, 0x8b44f7af);
    OP (C, D, A, B, 17, 0xffff5bb1);
    OP (B, C, D, A, 22, 0x895cd7be);
    OP (A, B, C, D,  7, 0x6b901122);
    OP (D, A, B, C, 12, 0xfd987193);
    OP (C, D, A, B, 17, 0xa679438e);
    OP (B, C, D, A, 22, 0x49b40821);

#undef OP
#define OP(f, a, b, c, d, k, s, T)  \
    do								      \
      { 							      \
	a += f (b, c, d) + correct_words[k] + T;		      \
	a = rol(a, s);						      \
	a += b; 						      \
      } 							      \
    while (0)

    /* Round 2.  */
    OP (FG, A, B, C, D,  1,  5, 0xf61e2562);
    OP (FG, D, A, B, C,  6,  9, 0xc040b340);
    OP (FG, C, D, A, B, 11, 14, 0x265e5a51);
    OP (FG, B, C, D, A,  0, 20, 0xe9b6c7aa);
    OP (FG, A, B, C, D,  5,  5, 0xd62f105d);
    OP (FG, D, A, B, C, 10,  9, 0x02441453);
    OP (FG, C, D, A, B, 15, 14, 0xd8a1e681);
    OP (FG, B, C, D, A,  4, 20, 0xe7d3fbc8);
    OP (FG, A, B, C, D,  9,  5, 0x21e1cde6);
    OP (FG, D, A, B, C, 14,  9, 0xc33707d6);
    OP (FG, C, D, A, B,  3, 14, 0xf4d50d87);
    OP (FG, B, C, D, A,  8, 20, 0x455a14ed);
    OP (FG, A, B, C, D, 13,  5, 0xa9e3e905);
    OP (FG, D, A, B, C,  2,  9, 0xfcefa3f8);
    OP (FG, C, D, A, B,  7, 14, 0x676f02d9);
    OP (FG, B, C, D, A, 12, 20, 0x8d2a4c8a);

    /* Round 3.  */
    OP (FH, A, B, C, D,  5,  4, 0xfffa3942);
    OP (FH, D, A, B, C,  8, 11, 0x8771f681);
    OP (FH, C, D, A, B, 11, 16, 0x6d9d6122);
    OP (FH, B, C, D, A, 14, 23, 0xfde5380c);
    OP (FH, A, B, C, D,  1,  4, 0xa4beea44);
    OP (FH, D, A, B, C,  4, 11, 0x4bdecfa9);
    OP (FH, C, D, A, B,  7, 16, 0xf6bb4b60);
    OP (FH, B, C, D, A, 10, 23, 0xbebfbc70);
    OP (FH, A, B, C, D, 13,  4, 0x289b7ec6);
    OP (FH, D, A, B, C,  0, 11, 0xeaa127fa);
    OP (FH, C, D, A, B,  3, 16, 0xd4ef3085);
    OP (FH, B, C, D, A,  6, 23, 0x04881d05);
    OP (FH, A, B, C, D,  9,  4, 0xd9d4d039);
    OP (FH, D, A, B, C, 12, 11, 0xe6db99e5);
    OP (FH, C, D, A, B, 15, 16, 0x1fa27cf8);
    OP (FH, B, C, D, A,  2, 23, 0xc4ac5665);

    /* Round 4.  */
    OP (FI, A, B, C, D,  0,  6, 0xf4292244);
    OP (FI, D, A, B, C,  7, 10, 0x432aff97);
    OP (FI, C, D, A, B, 14, 15, 0xab9423a7);
    OP (FI, B, C, D, A,  5, 21, 0xfc93a039);
    OP (FI, A, B, C, D, 12,  6, 0x655b59c3);
    OP (FI, D, A, B, C,  3, 10, 0x8f0ccc92);
    OP (FI, C, D, A, B, 10, 15, 0xffeff47d);
    OP (FI, B, C, D, A,  1, 21, 0x85845dd1);
    OP (FI, A, B, C, D,  8,  6, 0x6fa87e4f);
    OP (FI, D, A, B, C, 15, 10, 0xfe2ce6e0);
    OP (FI, C, D, A, B,  6, 15, 0xa3014314);
    OP (FI, B, C, D, A, 13, 21, 0x4e0811a1);
    OP (FI, A, B, C, D,  4,  6, 0xf7537e82);
    OP (FI, D, A, B, C, 11, 10, 0xbd3af235);
    OP (FI, C, D, A, B,  2, 15, 0x2ad7d2bb);
    OP (FI, B, C, D, A,  9, 21, 0xeb86d391);

    /* Put checksum in context given as argument.  */
    ctx->A += A;
    ctx->B += B;
    ctx->C += C;
    ctx->D += D;
}



/* The routine updates the message-digest context to
 * account for the presence of each of the characters inBuf[0..inLen-1]
 * in the message whose digest is being computed.
 */
static void
md5_write( MD5_CONTEXT *hd, byte *inbuf, size_t inlen)
{
    if( hd->count == 64 ) { /* flush the buffer */
	transform( hd, hd->buf );
        burn_stack (80+6*sizeof(void*));
	hd->count = 0;
	hd->nblocks++;
    }
    if( !inbuf )
	return;
    if( hd->count ) {
	for( ; inlen && hd->count < 64; inlen-- )
	    hd->buf[hd->count++] = *inbuf++;
	md5_write( hd, NULL, 0 );
	if( !inlen )
	    return;
    }

    while( inlen >= 64 ) {
	transform( hd, inbuf );
	hd->count = 0;
	hd->nblocks++;
	inlen -= 64;
	inbuf += 64;
    }
    burn_stack (80+6*sizeof(void*));
    for( ; inlen && hd->count < 64; inlen-- )
	hd->buf[hd->count++] = *inbuf++;
}



/* The routine final terminates the message-digest computation and
 * ends with the desired message digest in mdContext->digest[0...15].
 * The handle is prepared for a new MD5 cycle.
 * Returns 16 bytes representing the digest.
 */

static void
md5_final( MD5_CONTEXT *hd )
{
    u32 t, msb, lsb;
    byte *p;

    md5_write(hd, NULL, 0); /* flush */;

    t = hd->nblocks;
    /* multiply by 64 to make a byte count */
    lsb = t << 6;
    msb = t >> 26;
    /* add the count */
    t = lsb;
    if( (lsb += hd->count) < t )
	msb++;
    /* multiply by 8 to make a bit count */
    t = lsb;
    lsb <<= 3;
    msb <<= 3;
    msb |= t >> 29;

    if( hd->count < 56 ) { /* enough room */
	hd->buf[hd->count++] = 0x80; /* pad */
	while( hd->count < 56 )
	    hd->buf[hd->count++] = 0;  /* pad */
    }
    else { /* need one extra block */
	hd->buf[hd->count++] = 0x80; /* pad character */
	while( hd->count < 64 )
	    hd->buf[hd->count++] = 0;
	md5_write(hd, NULL, 0);  /* flush */;
	memset(hd->buf, 0, 56 ); /* fill next block with zeroes */
    }
    /* append the 64 bit count */
    hd->buf[56] = lsb	   ;
    hd->buf[57] = lsb >>  8;
    hd->buf[58] = lsb >> 16;
    hd->buf[59] = lsb >> 24;
    hd->buf[60] = msb	   ;
    hd->buf[61] = msb >>  8;
    hd->buf[62] = msb >> 16;
    hd->buf[63] = msb >> 24;
    transform( hd, hd->buf );
    burn_stack (80+6*sizeof(void*));

    p = hd->buf;
#ifdef BIG_ENDIAN_HOST
#define X(a) do { *p++ = hd-> a      ; *p++ = hd-> a >> 8;      \
		      *p++ = hd-> a >> 16; *p++ = hd-> a >> 24; } while(0)
#else /* little endian */
#define X(a) do { *(u32*)p = hd-> a ; p += 4; } while(0)
#endif
    X(A);
    X(B);
    X(C);
    X(D);
#undef X

}

static byte *
md5_read( MD5_CONTEXT *hd )
{
    return hd->buf;
}

/****************
 * Return some information about the algorithm.  We need algo here to
 * distinguish different flavors of the algorithm.
 * Returns: A pointer to string describing the algorithm or NULL if
 *	    the ALGO is invalid.
 */
const char *
md5_get_info( int algo, size_t *contextsize,
	       byte **r_asnoid, int *r_asnlen, int *r_mdlen,
	       void (**r_init)( void *c ),
	       void (**r_write)( void *c, byte *buf, size_t nbytes ),
	       void (**r_final)( void *c ),
	       byte *(**r_read)( void *c )
	     )
{
    static byte asn[18] = /* Object ID is 1.2.840.113549.2.5 */
		    { 0x30, 0x20, 0x30, 0x0c, 0x06, 0x08, 0x2a, 0x86,0x48,
		      0x86, 0xf7, 0x0d, 0x02, 0x05, 0x05, 0x00, 0x04, 0x10 };

    if( algo != 1 )
	return NULL;

    *contextsize = sizeof(MD5_CONTEXT);
    *r_asnoid = asn;
    *r_asnlen = DIM(asn);
    *r_mdlen = 16;
    *(void  (**)(MD5_CONTEXT *))r_init		       = md5_init;
    *(void  (**)(MD5_CONTEXT *, byte*, size_t))r_write = md5_write;
    *(void  (**)(MD5_CONTEXT *))r_final 	       = md5_final;
    *(byte *(**)(MD5_CONTEXT *))r_read		       = md5_read;

    return "MD5";
}
